The purpose of this work is to investigate various biological and chemical properties of two types of murine cell surface antigens that induce graft rejection: histocompatibility antigens (H-2) and tumor associated transplantation antigens (TATA). In the case of TATAs, the approach is to purify and characterize the molecules bearing these antigens from tumor cells. Polyclonal and monoclonal antibodies and specific T cell clones that recognize these molecules may then be prepared and used to investigate their biological properties. Ultimately, the amino acid sequence of these proteins will be determined and suitable DNA probes can be prepared and used to study the genes which encode the molecules. This structural information will lead to an understanding of the mechanism of induction of these antigens and their relationship to the oncogenic process. The structure of these molecules may also provide insights into some of the unique immunogenic properties of tumors, e.g., their ability to escape an apparently strong antitumor immune response. In the case of H-2 antigens, the approach is to identify class I molecules expressed by tumor cells and determine which of the many class I genes encode them. Alloantisera, monoclonal antibodies and xenoantisera directed against H-2 molecules are used to purify and characterize the proteins. Specific DNA probes and molecular cloning techniques are then used to identify the mRNA and genes that encode these H-2 molecules. This work is aimed toward understanding any special role that H-2 molecules might have in tumor cell biology and anti-tumor immunity. The results also contribute to an understanding of the organization and evolution of the class I multigene family.